What is incident management?

Incident is an event that may lead to loss or disruption to an organization in operation; if the incident didn't managed well it might escalate and make more damage to the organization.
So incident management is the proactive process that should be followed to limit the effect of such event

The main role of Incident Management is to restore the service to its standard operations as quickly as possible by monitoring and managing the progress of all incidents, retaining ownership of them until a work-around solution or permanent fix has been found.
Incident Management is part of the ITIL v3 Service Operations publication

The process of responding to an unplanned event to first, mitigate its consequences and thereby finding out what factors caused or contributed to the event; and ensuring that such event does not reoccur.